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I can reproduce the segfault on F16:
Python 3.3.0a0 (default:3828d93fd330, Feb 23 2012, 13:49:57) 
[GCC 4.4.6] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> d = {'__qualname__':'XXX'}
[66934 refs]
>>> T = type('foo', (), d)
[66956 refs]
>>> T
python: Objects/unicodeobject.c:301: _PyUnicode_CheckConsistency: Assertion `((((((PyObject*)(op))->ob_type))->tp_flags & ((1L<<28))) != 0)' failed.
Aborted (core dumped)
The patch looks mostly OK, but I can still segfault the interpreter by using a '__qualname__' of 'None':
Python 3.3.0a0 (default:3828d93fd330+, Feb 23 2012, 13:55:57) 
[GCC 4.4.6] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> d = {'__qualname__':'XXX'}
[67128 refs]
>>> T = type('foo', (), d)
[67156 refs]
>>> T
<class '__main__.XXX'>
[67161 refs]
>>> d = {'__qualname__': None}
[67161 refs]
>>> T = type('foo', (), d)
[67185 refs]
>>> T
python: Objects/unicodeobject.c:301: _PyUnicode_CheckConsistency: Assertion `((((((PyObject*)(op))->ob_type))->tp_flags & ((1L<<28))) != 0)' failed.
Aborted (core dumped)
Try this additional unit test:
 d = {'__qualname__': None}
 tp = type('foo', (), d)
 self.assertEqual(tp.__qualname__, None)
 self.assertEqual(tp.__dict__['__qualname__'], None)
 self.assertEqual(d, {'__qualname__': None})
 self.assertTrue(repr(tp))